TROUBLESHOOTING
In order to improve FL Studio for better usability and feature set, some changes are introduced through the various releases which might be incompatible with projects created in earlier versions of FruityLoops.
NOTE: "FruityLoops" is the name of the basic software package that only existed in previous versions. The current releases are called FL Studio and come in 3 flavors: Express Edition, FruityLoops Edition and Producer Edition.
In earlier releases, the lack of sequence in the Playlist caused FruityLoops to play all patterns in the song in sequential order. FL Studio 4 doesn't have that feature anymore. You need to order the patterns manually in the Playlist window to achieve the same effect.
Some of the precomputed effects in the Sampler Channel Settings tab are deprecated in FL Studio and were hidden or replaced by better alternatives. However, for compatibility reasons, FL Studio still supports those legacy effects. To see them, turn on Show Legacy Precomputed Effects in your General Settings window.
In earlier releases, the project's time signature was defined as a number of steps per bar and number of steps per beat. This allowed for wrong time signatures, for example, ending a bar with half the steps from a new beat.
The current release defines time signature as a number of steps per beat and number of beats per bar. For compatibility with older projects that use non-standard time signatures, the beat steps are set to 1 to preserve the song structure.
Earlier releases had an option to turn off the logarithmic volume mapping and use linear mapping instead. The current release has logarithmic levels as a hard coded characteristic of the mixing engine.
Older projects that use linear volume mapping switch to logarithmic levels when opened in the new version of FL Studio.
FL Studio 3.5 doesn't support custom channel name color. Channel name colors in older projects are ignored. However, you can change the color of a channel button from the Channel Settings window.
NOTE: FL Studio 3.5 will load and play older projects without problems no matter if they include or not incompatible features.
You can upgrade to FL Studio 4 and still work with an older release to finish old projects, to avoid any compatibility issues. The registration information of FL Studio will not overwrite registration information of older releases.
To do that, before upgrading to FL Studio, ensure you have your earlier release installed properly with all plugins you need to have (don't install the plugins released with FL Studio on earlier FruityLoops release, because they might not be compatible). Then install FL Studio and its plugins in another folder. Your earlier FruityLoops release will retain its own registration and settings independently of FL Studio.